docs: def voidage_experimental(m, rho, D, H):
      r'''Calculates voidage of a bed or mesh given an experimental weight and
      fixed density, diameter, and height, as shown in [1]_. The formula is also
      self-evident.
  
      .. math::
          \epsilon = 1 - \frac{\frac{m_{mesh}}{\frac{\pi}{4}d_{column}^2
          L_{mesh}}}{\rho_{material}}
  
      Parameters
      ----------
      m : float
          Mass of mesh or bed particles weighted, [kg]
      rho : float
          Density of solid particles or mesh [kg/m^3]
      D : float
          Diameter of the cylindrical bed [m]
      H : float
          Height of the demister or bed [m]
  
      Returns
      -------
      voidage : float
          Voidage of bed of the material []
  
      Notes
      -----
      Should be trusted over manufacturer data.
  
      Examples
      --------
      >>> voidage_experimental(m=126, rho=8000, D=1, H=1)
      0.9799464771704212
  
      References
      ----------
      .. [1] Helsør, T., and H. Svendsen. "Experimental Characterization of
         Pressure Drop in Dry Demisters at Low and Elevated Pressures." Chemical
         Engineering Research and Design 85, no. 3 (2007): 377-85.
         doi:10.1205/cherd06048.
      '''
      return 1 - m/(pi/4*D**2*H)/rho